Ballistic injection for gas chromatography

ABSTRACT

An automatic sample injector for injecting discrete samples of a heat expansible material into a gas chromatographic unit. Sample capsules are successively conducted to a capsule ram which forces the capsules up an inclined passageway where these capsules are heated. The sample material expands upon heating, and is carried in vaporized form by a carrier gas to a gas chromatograph. The capsule ram is withdrawn down the inclined passageway past a discharge conduit where the component parts of the sample capsule fall into a collection area.

United States Patent [19 Fox et al.

[ 11 3,759,107 1 Sept. 18,1973

BALLISTIC INJECTION FOR GAS CHROMATOGRAPHY Stewart A. Fox, Lyons; Robert J. Magill, .Barrington, both of 111.

G. D. Searle & Co., Chicago, 111.

Oct. 5, 1972 [75] Inventors:

Assignee:

Filed:

Appl. No.:

U.S. Cl 73/422 GC Int. Cl. G011! 31/38 Field of Search 73/422 GC, 23.1;

References Cited UNITED STATES PATENTS 3/1965 Varadi et al...... 73/23.l 3/1970 Kim et al 73/422 GC OTHER PUBLICATIONS Podmore, Journal of Chromatography, Vol. 20 (1965),

CARRIER GAS SOURCE pp. 131-134,QD241J5.

Primary Examiner-S. Clement Swisher Attorney-Lowell C. Bergstedt et al.

[57] ABSTRACT An automatic sample injector for injecting discrete samples of a heat expansible material into a gas chromatographic unit. Sample capsules are successively conducted to a capsule ram which forces the capsules up an inclined passageway where these capsules are heated. The sample material expands upon heating, and is carried in vaporized form by a carrier gas to a gas chromatograph. The capsule ram is withdrawn down the inclined passageway past a discharge conduit where the component parts of the sample capsule fall into a collection area.

7 Claims, 3 Drawing Figures 1. BALLIS'IIC INJECTION FOR GAS CHROMATOGRAPHY This invention relates to a sample injector for automatically injecting discrete samples of a heat expansible material into a gas chromatograph. Each of the discrete samples is successively moved to an injection position where heating of the sample capsule occurs. The sample material to be analyzed expands upon heating and escapes from the sample capsule. The sample material is carried in vaporized form in a continuous carrier gas stream to the gas chromatograph. The capsule ram is then withdrawn to allow the pieces of the capsule to fall into a collection receptacle.

I-Ieretofore, discrete samples of a heat expansible material have been injected into a gas chromatograph using conventional injection systems which have been unreliable and which have lacked a sufficient degree of reproducability of results. An example of such a system is illustrated in U. S. Pat. No. 3,401,552. In this injector, sample capsules are dropped into a wire mesh basket in a sample heating zone. The samples are heated causing the sample material to vaporize and escape from the capsules. A carrier gas stream carries the sample to be analyzed through the mesh of the basket to the gas chromatograph, leaving the component pieces of the sample capsule trapped in the basket. While injection is achieved to a degree, there is a tendency in this system for the sample material to become entrapped in the concave portions of the capsule components in the basket. This prevents portions of the material from being analyzed and thereby distorts the results of chromatographic analysis. In addition, the basket is rather inaccessible for the purpose of removingcapsule components. This removal can be accomplished only after a lengthy interruption to the operation of the injector. Furthermore, the area within which the sample to be analyzed may circulate prior to being carried into the gas chromatograph is quite large, thereby creating a loss of peak resolution.

It is an object of the present invention to obviate these defects in conventional systems by providing an injection system which directs the sample material to be analyzed toward an outlet to the gas chromatograph. In addition, the area within which the sample material to be analyzed is allowed to circulate prior to being carried to the gas chromatograph is much smaller than in conventional systems. Also, the component portions of the spent sample capsules are immediately removed from the injector system, thereby posing no erratic entrapment of the sample material to be analyzed.

In a broad aspect this invention is a sample injector for automatically injecting discrete samples into a gas chromatograph comprising: a sample dispensing means for sequentially dispensing capsules each containing a discrete heat expansible sample of material to be analyzed in a gas chromatograph; an elongated ram passageway inclined with respect to the vertical having an at the upper end thereof for mating with the sealing surface of said ram passageway, in sliding engagement with said ram passageway; a carrier gas source for continuously forcing carrier gas through the upper end of said ram passageway into said gas chromatograph; and heating means for heating a capsule moved automatically to said upper end of said ram passageway by said ram, whereby the aforesaid expansible material escapes from said capsule and is carried into said gas chromatograph by said carrier gas.

The accompanying drawings illustrate a preferred embodiment of this invention, in which:

FIG. 1 is a sectional elevational view of the invention,

FIG. 2 is a cross sectional view of the invention taken at the lines 2-2 of FIG. 1, and

FIG. 3 is an enlarged view of the upper end of the capsule ram of FIG. 1.

A sample injector 10 is provided with a sample dispensing means 11, an elongated ram passageway 17, a capsule receptacle means 42, a capsule ram 30, and a heating means 23 in the form of electrical resistance heating coils.

The sample dispensing means 11 is comprised of a shaft 12 which rotates in a series of periodic advances about a vertical axis, carrying with it a disc 14. Disc 14 has axial apertures located at uniform intervals at a predetermined radial distance from its center. In each of the apertures is located a sample capsule 41 containing a discrete heat expansible sample of material to be analyzed in the gas chromatograph. This material may be either a liquid or a solid which vaporized upon heating, or a gas which expands with heating. Typically, the capsules 41 are sealed with a plug of teflon or other material. In some instances, however, metal capsules may be purposefully left unplugged prior to injection in order that the solvent used may be evaporated before loading of the sample. This may be done to obviate a difficulty in interpreting the chromatograph reading which difficulty might result from using a solvent. In any event, as the shaft 12 periodically advances in its rotational movement, each of the sample capsules 41 are positioned above a single axial aperture in the sample supporting table 13. This single aperture is located at the same radial distance from the center of the sample dispensing means as are the sample capsules 41. As each of the sample capsules 41 is moved above the aperture in table 13, the force of gravity causes the sample capsule 41 to fall downward through a connecting tube 15 into a loading conduit 16. The lower end of the loading conduit 16 terminates at an intermediate loading opening 21 in the elongated ram passageway 17.

A carrier gas inlet tube 39 is connected through a channel in the dispensing means 11 to the loading conduit 16. A carrier gas source, indicated at 45, supplies carrier gas through tube 39. The carrier gas flows down through connecting tube 15 and loading conduit 16, through loading opening 21, and up through the ram passageway 17 and through the outlet connection 24 to the gas chromatograph as long as loading opening 21 is not blocked.

Ram passageway 17 is constructed of a hollow glass tube inclined at an angle, preferably about 30, with respect to the vertical. The angle of 30 is selected as the steepest inclination which can be formed with conventional glass working procedures, though the ram passageway 17, the loading conduit 16, and the discharge conduit 20 are not necessarily of unitary construction.

In addition to the intermediate loading opening 21, which is in communication with the sample dispensing means 11 by means of the loading conduit 16, the ram passageway 17 also has an upper end 18, a lower end 19, a sealing surface A, and a discharge opening 22 located at an intermediate point along the ram passageway 17, but longitudinally displaced from and below the loading opening 21.

A capsule receptacle means 42 is in communication with the ram passageway 17 at the discharge opening 22. The capsule receptacle means includes the discharge conduit extending vertically downward from discharge opening 22. It should be noted that the inner diameter of the discharge conduit 20 is preferably larger than the inner diameter of the loading conduit 16. When sealed capsules are used, it is possible that the capsule components may be deformed when the sample to be analyzed escapes from them. These deformed capsule parts might become jammed in the discharge conduit 20 if the diameter thereof is not sufficiently large. The capsule receptacle means 42 is further comprised of plastic fittings 36 and 37 and silicone rubber gasket 38 which together form a seal with a collection receptacle 40.

It can be seen that when the capsule ram 30 is at its uppermostposition during the injection phase of the injection cycle, the outer surface of the capsule ram 30 will block the loading opening 20, as well as the discharge opening 22. It is for this reason that a second, alternate path of carrier gas flow is desirable. This path is provided from the carrier gas source 45 through the carrier gas inlet 34. An axial aperture is formed in the fitting 33 which is attached to the mating fitting 32 at the lower end 19 of the ram passageway 17. A mating axial aperture exists through the silicone rubber gasket 35 at lower end 19. A carrier gas passage 13 extends axially through the capsule ram 30 to communicate with the upper end 18 of the ram passageway 17. This axial passage 43 is constricted just adjacent to the upper end of the ram 30 as best illustrated in FIG. 3, so as to provide a maximum carrier gas velocity at this point. It can be seen then that even with the capsule ram 30 in its uppermost position blocking loading opening 20, a pathway for carrier gas flow exists since two paths of carrier gas flow are provided in the system, with roughly equal volumes of carrier gas being passed through each path when both paths are open.

The capsule ram 30 is comprised of an elongated, annular glass rod 46 with an axial gas passage 43 extending therethrough. A magnetizeable element in the form of an annular iron structure 31 is positioned around the lower extremity of the annular glass rod 46. Element 31 slides within the lower end 19 of ram passageway 17, but will not pass above the constricted section indicated at B in the ram passageway.

The face of the upper end of the glass rod 46 of capsule ram 30 is chamfered at the sealing surface denoted at F. It can be seen that this portion F of capsule ram 30 will not pass into the constricted upper end 18 of the ram passageway 17 above the mating sealing surface A of ram passageway 17. When the ram 30 is forced to its uppermost position in the ram passageway 17, the mating sealing surfaces A and F prevent any of the contents of the capsules 41 from passing back down into the lower portions of ram passageway 17 Normally, a gas tight fit is obtained between the sealing surfaces A and F by lapping these surfaces together during the construction of the injection system of this invention. The 7 interface formed between the sealing surfaces A and F is in the sahpe of a frustum of a cone. Preferably, the sealing surfaces A and F each lie at a 45 angle with respect to the axis of the ram passageway 17. One alternative form of the sealing surfaces depicted would be a construction where the upper face of glass rod 46 would butt up against a ledge in ram passageway 17. The illustrated construction forms a better seal as compared to such an arrangement, however.

Dual electromagnets or solenoids 26 and 27 are positioned longitudinally adjacent to each other and coaxially about a portion of a lower end 19 of the ram passageway 17. By actuating the solenoids 26 and 27 in varying combinations, a magnetic field acts on the magnetizeable element 31, thereby driving the entire capsule ram 30 toward the upper end of the ram passageway 17. This driving force acts to move the ram 30 to controlled positions obstructing either the discharge opening 22 alone, or both the discharge opening 22 and the loading opening 21. When both of the electromagnetics 26 and 27 are deactivated, gravity causes the capsule ram 30 to move to an extreme downward position away from the upper end 13 of the ram passageway 17 with the magnetizeable element 31 resting against the rubber gasket 35 and with neither of the openings 21 or 22 obstructed. It is in this position that the sample capsule components 41 are able to fall from the upper end 18 of the ram passageway through the discharge opening 22 and into the receptacle 40.

In the operation of .this invention, at the start of each sample injection cycle, the solenoid 26 is actuated by a current source acting through electrical leads 29, so that the ram 30 is positioned with its upper face positioned as indicated in the drawing. The shaft 12 turns the disc 14 so that a sealed capsule 41 plunges down through the loading conduit 16. As the sample 41 falls through the loading opening 21 into the ram passageway 17, it assumes the position illustrated. Thereafter, the second solenoid 27 is actuated by means of electrical leads 28, with the first solenoid 26 remaining in an actuated condition. This forces the ram 311 up the sloping ram passageway 17 until a seal is formed between the sealing surfaces A and F. This seal is enhanced by the iron ring 47 positioned at the upper end of solenoid 27 to act as a flux gate. This tends to increase the force holding the sealing surfaces A and F together. Electrical current is passed through leads 44 so that resistance heater 23 heats the sealed capsule 41 until the heat expansible sample material ruptures the seal of the capsule, and escapes therefrom if a sealed capsule is used. If an unsealed capsule is used, the heat expansible sample material vaporizes without rupturing the capsule. A transverse cross bar 25, illustrated in FIG. 2, is positioned near the upper extremity of the upper end 18 of the ram passageway 17. This single cross member 25 allows the carrier gas to flow freely, but prevents any portion of the capsule or any teflon plug from obstructing the outlet 24. The carrier gas eminating from the passage 43 in the ram 30 carries the sample to be analyzed through the gas outlet 24, which is typically heated by a detector block which is not shown in FIG. 1 for the sake of clarity of illustration. Both of the solenoids 26 and 27 are thereafter de-energized, thereby allowing the ram 30 to fall to its extreme lower position with the face of the upper end of rod 416 at the position D. The components parts 41 of the sample capsule follow the capsule ram 30 down the passageway 17 and cle 40. Thereafter, the solenoid 26 is actuated and a new sample injection cycle is begun.

The foregoing disclosure and description of the invention is illustrative and explanatory thereof, and various changes in the size, shape or materials as well as in the detail of the illustrated embodiment, may be made within the scope of the appended claims but without departing from the principle of the invention.

We claim:

1. A sample injector for automatically injecting discrete samples into agas chromatograph comprising:

a. a sample dispensing means for sequentially dispensing capsules each containing a discrete heat expansible sample of material to be analyzed in a gas chromatograph,

b. an elongated ram passageway inclined with respect to the vertical having an upper end in communication with a gas chromatograph and having an intermediate loading opening in communication with said sample dispensing means, and having a sealing surface located between said upper end and said loading opening,

c. a capsule receptacle means below the upper end of said ram passageway and in communication with said ram passageway at a discharge opening longitudinally displaced from and below the aforesaid loading opening,

d. a capsule ram having a sealing surface at the upper end thereof for mating with the sealing surface of said ram passageway in sliding engagement with said ram passageway,

e. a carrier gas source for continuously forcing carrier gas through the upper end of said ram passageway into said gas chromatograph, and

f. heating means for heating a capsule moved automatically to said upper end of said ram passageway by said ram, whereby the aforesaid expansible material escapes from said capsule and is carried into said gas chromatograph by said carrier gas.

2. The apparatus of claim 1 further comprising a magnetizeable element as a portion of said capsule ram, and dual electromagnets positioned about at least a portion of the aforesaid ram passageway, whereby said capsule ram is driven toward the upper end of said ram passageway to selectively obstruct said discharge opening and said loading opening by the actuation of varying combinations of said dual electromagnets, and whereby gravity tends to cause said capsule ram to move downward away from the upper end of said ram passageway.

3. The apparatus of claim I further comprising a transverse cross member means near the upper extremity of said upper end of said ram passageway for preventing component portions of said capsule from passing into said gas chromatograph.

4. The apparatus of claim 1 wherein said ram passageway is inclined at an angle of 30 with respect to the vertical.

5. The apparatus of claim 1 wherein a carrier gas passage extends. axially thorugh said capsule ram to communicate with said upper end of said ram passageway, and said carrier gas source is connected to said carrier gas passage and to said loading opening in said ram passageway, thereby providing at least two paths of carrier gas flow.

6. The apparatus of claim 1 wherein the sealing surfaces of said capsule ram and said ram passageway are positionable at an interface in the shape of a frustum of a cone.

7. The apparatus of claim 6 wherein the sealing surfaces of said capsule ram and said ram passageway each lie at a 45 angle with respect to the axis of the ram pas- 

1. A sample injector for automatically injecting dis-crete samples into a gas chromatograph comprising: a. a sample dispensing means for sequentially dispensing capsules each containing a discrete heat expansible sample of mateRial to be analyzed in a gas chromatograph, b. an elongated ram passageway inclined with respect to the vertical having an upper end in communication with a gas chromatograph and having an intermediate loading opening in communication with said sample dispensing means, and having a sealing surface located between said upper end and said loading opening, c. a capsule receptacle means below the upper end of said ram passageway and in communication with said ram passageway at a discharge opening longitudinally displaced from and below the aforesaid loading opening, d. a capsule ram having a sealing surface at the upper end thereof for mating with the sealing surface of said ram passageway in sliding engagement with said ram passageway, e. a carrier gas source for continuously forcing carrier gas through the upper end of said ram passageway into said gas chromatograph, and f. heating means for heating a capsule moved automatically to said upper end of said ram passageway by said ram, whereby the aforesaid expansible material escapes from said capsule and is carried into said gas chromatograph by said carrier gas.
 2. The apparatus of claim 1 further comprising a magnetizeable element as a portion of said capsule ram, and dual electromagnets positioned about at least a portion of the aforesaid ram passageway, whereby said capsule ram is driven toward the upper end of said ram passageway to selectively obstruct said discharge opening and said loading opening by the actuation of varying combinations of said dual electromagnets, and whereby gravity tends to cause said capsule ram to move downward away from the upper end of said ram passageway.
 3. The apparatus of claim 1 further comprising a transverse cross member means near the upper extremity of said upper end of said ram passageway for preventing component portions of said capsule from passing into said gas chromatograph.
 4. The apparatus of claim 1 wherein said ram passageway is inclined at an angle of 30* with respect to the vertical.
 5. The apparatus of claim 1 wherein a carrier gas passage extends axially thorugh said capsule ram to communicate with said upper end of said ram passageway, and said carrier gas source is connected to said carrier gas passage and to said loading opening in said ram passageway, thereby providing at least two paths of carrier gas flow.
 6. The apparatus of claim 1 wherein the sealing surfaces of said capsule ram and said ram passageway are positionable at an interface in the shape of a frustum of a cone.
 7. The apparatus of claim 6 wherein the sealing surfaces of said capsule ram and said ram passageway each lie at a 45* angle with respect to the axis of the ram passageway. 